Check file handle in C using system calls

chp2/fopenflags.c

@@ -0,0 +1,30 @@
+#include <stdio.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <errno.h>
+
+int main(void)
+{
+	int fd;
+	fd = open("test.txt", O_CREAT | O_EXCL);
+	if (fd == -1)
+		perror("First open");
+	close(fd);
+
+	fd = open("test.txt", O_CREAT | O_EXCL);
+	if (fd == -1)
+		perror("Second open");
+	close(fd);
+
+	fd = open("test.txt", O_CREAT | O_EXCL);
+	if (fd == -1)
+		perror("Third open");
+	close(fd);
+	
+	fd = open("test.txt", O_CREAT);
+	if (fd == -1)
+		perror("Fourth open");
+	close(fd);
+
+	return 0;
+}

chp2/fopenmode.c

@@ -0,0 +1,15 @@
+#include <stdio.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <errno.h>
+
+int main(void)
+{
+	int fd;
+	fd = open("test.txt", O_CREAT | O_EXCL, S_IWUSR | S_IRUSR | S_IRGRP | S_IROTH);
+	if (fd == -1)
+		perror("open");
+	close(fd);
+
+	return 0;
+}

chp2/fpread.c

@@ -0,0 +1,56 @@
+#include <errno.h>
+#include <fcntl.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <string.h>
+#define _XOPEN_SOURCE 500
+#include <unistd.h>
+
+int main(void) {
+  printf("Try to open file read.txt\n");
+  int fd = open("read.txt", O_RDONLY);
+  if (fd == -1) {
+    perror("Failed to open read.txt");
+    return -1;
+  }
+  printf("Open file success\n");
+
+  int len;
+  // move file's cursor at the end of file and return bytes
+  if ((len = lseek(fd, 0, SEEK_END)) == -1) {
+    perror("Failed to move cursor at end of read.txt file");
+    return -1;
+  }
+
+  // cannot rewind cursor at the start file because pread use "bytes_read_total" for position
+
+  printf("File size of %d bytes\n", len);
+
+  printf("Reading file read.txt\n");
+  char buf[len + 1];
+  memset(buf, 0, sizeof(buf));
+
+  size_t bytes_read_total = 0;
+  ssize_t ret;
+  while (bytes_read_total < len && (ret = pread(fd, buf, len - bytes_read_total, bytes_read_total)) != -1) {
+    if (ret == -1) {
+      if (errno == EINTR) continue;
+      perror("Failed to read read.txt");
+      break;
+    }
+    bytes_read_total += ret;
+  }
+
+  buf[bytes_read_total] = '\0';
+
+  printf("File text is:\n\"%s\"\n", buf);
+
+  printf("Close file read.txt\n");
+  
+  if (close(fd) == -1) {
+    perror("Failed to close read.txt");
+    return -1;
+  }
+
+  return 0;
+}

chp2/fread.c

@@ -0,0 +1,55 @@
+#include <errno.h>
+#include <fcntl.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int main(void) {
+  printf("Try to open file read.txt\n");
+  int fd = open("read.txt", O_RDONLY);
+  if (fd == -1) {
+    perror("Failed to open read.txt");
+    return -1;
+  }
+  printf("Open file success\n");
+
+  int len;
+  if ((len = lseek(fd, 0, SEEK_END)) == -1) {
+    perror("Failed to move cursor at end of read.txt file");
+    return -1;
+  }
+  printf("File size of %d bytes\n", len);
+  if (lseek(fd, 0, SEEK_SET) == -1) {
+    perror("Failed to move cursor at start of read.txt file");
+    return -1;
+  }
+
+  printf("Reading file read.txt\n");
+  char buf[len + 1];
+  memset(buf, 0, sizeof(buf));
+
+  size_t bytes_read_total = 0;
+  ssize_t ret;
+  while (bytes_read_total < len && (ret = read(fd, buf + bytes_read_total, len - bytes_read_total)) != 0) {
+    if (ret == -1) {
+      if (errno == EINTR) continue;
+      perror("Failed to read read.txt");
+      break;
+    }
+    bytes_read_total += ret;
+  }
+
+  buf[bytes_read_total] = '\0';
+
+  printf("File text is:\n\"%s\"\n", buf);
+
+  printf("Close file read.txt\n");
+  
+  if (close(fd) == -1) {
+    perror("Failed to close read.txt");
+    return -1;
+  }
+
+  return 0;
+}

chp2/ftruncate.c

@@ -0,0 +1,13 @@
+#include <unistd.h>
+#include <stdio.h>
+
+int main(void) {
+	int ret;
+
+	ret = truncate("./pirate.txt", 45);
+	if (ret == -1) {
+		perror("truncate");
+		return -1;
+	}
+	return 0;
+}

chp2/pirate.txt

@@ -0,0 +1,2 @@
+Edward Teach was a notorious English pirate.
+He was nicknamed Blackbeard.

chp2/poll.c

@@ -0,0 +1,38 @@
+#include <stdio.h>
+#include <unistd.h>
+#include <poll.h>
+
+#define TIMEOUT 5  /* poll timeout, in seconds */
+
+int main(void) {
+	struct pollfd fds[2];
+	int ret;
+
+	/* watch stdin for input */
+	fds[0].fd = STDIN_FILENO;
+	fds[0].events = POLLIN;
+
+	/* watch stdout for ability to write (almost always true) */
+	fds[1].fd = STDOUT_FILENO;
+	fds[1].events = POLLOUT;
+
+	/* All set, block! */
+	ret = poll(fds, 2, TIMEOUT * 1000);
+	if (ret == -1) {
+		perror("poll");
+		return 1;
+	}
+
+	if (!ret) {
+		printf("%d seconds elapsed.\n", TIMEOUT);
+		return 0;
+	}
+
+	if (fds[0].revents & POLLIN)
+		printf("stdin is readable\n");
+	
+	if (fds[1].revents & POLLOUT)
+		printf("stdout is writable\n");
+
+	return 0;
+}

chp2/read.txt

@@ -0,0 +1 @@
+Hello, World!

chp2/select.c

@@ -0,0 +1,65 @@
+#include <stdio.h>
+#include <sys/time.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#define TIMEOUT 5
+#define BUF_LEN 1024
+
+int main(void) {
+	struct timeval tv;
+	fd_set readfds;
+	int ret;
+
+	/* Wait on stdin for intput. */
+	FD_ZERO(&readfds);
+	FD_SET(STDIN_FILENO, &readfds);
+	
+	/* Wait up to file seconds */
+	tv.tv_sec = TIMEOUT;
+	tv.tv_usec = 0;
+
+	/* All right, now block! */
+	ret = select(
+		STDIN_FILENO + 1,
+		&readfds,
+		NULL,
+		NULL,
+		&tv
+	);
+	if (ret == -1) {
+		perror("select");
+		return 1;
+	} else if (!ret) {
+		printf("%d seconds elapsed.\n", TIMEOUT);
+		return 0;
+	}
+
+	/*
+	 * Is our file descriptor ready to read?
+	 * (It must be, as it was the only fd that
+	 * we provided and the call returned
+	 * nonzero, but we will humor ourselves.)
+	 */
+	if (FD_ISSET(STDIN_FILENO, &readfds)) {
+		char buf[BUF_LEN+1];
+		int len;
+
+		/* guaranteed to not block */
+		len = read(STDIN_FILENO, buf, BUF_LEN);
+		if (len == -1) {
+			perror("read");
+			return 1;
+		}
+
+		if (len) {
+			buf[len] = '\0';
+			printf("read: %s\n", buf);
+		}
+		
+		return 0;
+	}
+
+	fprintf(stderr, "This should not happen!\n");
+	return 1;
+}

chp2/select_regular_files.c

@@ -0,0 +1,132 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <errno.h>
+#include <string.h>
+#include <sys/time.h>
+#include <sys/select.h>
+
+#define FILE_NUMBER 3
+#define FILENAME_MAX_LEN 10
+#define TIMEOUT 10
+#define BUF_LEN 1024
+
+int create_tmp_file(char *filename);
+void cleanup(char *filenames[]);
+
+int main(void) {
+	int exit_code = 0;
+	char *filename_template = "test%d.txt";
+	char *filenames[FILE_NUMBER] = {NULL};
+	int fds[FILE_NUMBER] = {0};
+
+	// Create a bunch of number ephemeral files
+	for (int i = 0; i < FILE_NUMBER; i++) {
+		char *filename = (char *)malloc(FILENAME_MAX_LEN*sizeof(char)); 
+		if (!filename) {
+			perror("malloc failed");
+			exit_code = -1;
+			goto exit;
+		}
+		snprintf(filename, FILENAME_MAX_LEN, filename_template, i+1);
+		filenames[i] = filename;
+		printf("Opening file %s...\n", filename);
+		fds[i] = create_tmp_file(filename);
+		if (fds[i] == -1) {
+			fprintf(stderr, "Error to open file %s: %s\n", filename, strerror(errno));
+			exit_code = -1;
+			goto exit;
+		}
+		printf("Open file %s with file descriptor %d\n", filename, fds[i]);
+
+		// write something in the files
+		dprintf(fds[i], "Hello I am %s\n", filename);
+	}
+	
+	fd_set readfds;
+	FD_ZERO(&readfds);
+	for (int i = 0; i < FILE_NUMBER; i++) {
+		FD_SET(fds[i], &readfds);
+	}
+	
+	struct timeval *timeout = (struct timeval *)malloc(sizeof(struct timeval));
+	timeout->tv_sec = TIMEOUT;
+	timeout->tv_usec = 0;
+	
+	/* This function do not work with regular files because for the operating system,
+	 * a regular file is ready always.
+         * This example is wrong the best way to use select() is with socket, pipe or other channel types.
+	 */
+	int ret = select(
+		FILE_NUMBER + 1,
+		&readfds,
+		NULL,
+		NULL,
+		timeout
+	);
+
+	if (ret == -1) {
+		fprintf(stderr, "Error to select: %s\n", strerror(errno));
+		exit_code = 1;
+		goto exit;
+	} else if (!ret) {
+		fprintf(stderr, "%d seconds elapsed.\n", TIMEOUT);
+		exit_code = 1;
+		goto exit;
+	}
+
+	for (int i = 0; i < FILE_NUMBER; i++) {
+		int fd = fds[i];
+		if (FD_ISSET(fd, &readfds)) {
+			char buf[BUF_LEN+1];
+			int len = read(fd, buf, BUF_LEN);
+			if (len == -1) {
+				fprintf(stderr, "Error reading file %s: %s\n", filenames[i], strerror(errno));
+				exit_code = 1;
+				goto exit;
+			}
+			if (len) {
+				buf[len] = '\0';
+				printf("%s:\n%s\n", filenames[i], buf);
+			}
+		}
+	}
+
+exit:
+	// Closing and remove all creating files
+	for (int i = 0; i < FILE_NUMBER; i++) {
+		int fd = fds[i];
+		printf("Close file with file descriptor %d\n", fd);
+		if (close(fd) == -1) { 
+			fprintf(stderr, "Error to close file %d: %s\n", fd, strerror(errno));
+		}
+	}
+
+	free(timeout);
+	timeout = NULL;
+
+	printf("Cleanup files\n");
+	cleanup(filenames);
+	
+	return exit_code;
+}
+
+int create_tmp_file(char *filename) {
+	int fd = open(filename, O_CREAT | O_EXCL | O_RDWR, 0644);
+	if (fd == -1) {
+		return -1;
+	}
+	return fd;
+}
+
+void cleanup(char *filenames[]) {
+	for (int j = 0; j < FILE_NUMBER; j++) {
+		if (filenames[j] != NULL) {
+			if (remove(filenames[j]) == -1) 
+				fprintf(stderr, "Failed to remove %s: %s\n", filenames[j], strerror(errno));
+			free(filenames[j]);
+			filenames[j] = NULL;
+		}
+	}
+}